Shedding light on the nanoscale
carrier dynamics and photogeneration in Quantum Dot systems
Gianluca Grimaldi (TU Delft - ChemE/Opto-electronic Materials)
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Abstract
The generation of excited carrier via light absorption (photogeneration) and their ability to propagate in space in Quantum Dot (QD) films affect critically the performance of QD-based optoelectronic devices. The work performed in this thesis is aimed at increasing the understanding of fundamental processes occurring in QD solutions and QD films, providing the groundwork for future optimization of QD-based devices.
We employed a combination of ultrafast spectroscopy techniques (transient absorption spectroscopy and spectroelectrochemistry) and computational methods (Monte-Carlo and Density Functional Theory simulations), to obtain information about the energy of electronic levels and the dynamics of carrier transport, relaxation and transfer between different materials. Our results provide evidence of previously unreported effects: hot-electron transfer between different QD species, a hole contribution to the bleach of cadmium chalcogenide QDs and the presence of a temperature de-activated mobility for carrier hopping in InP QD films. Furthermore, we demonstrate the possibility to achieve band-alignment in QD heterojunction via control of the ligand passivation on the QD
surface.